The present invention relates to a hammer drill. More particularly, it relates to a hammer drill which has a guiding cylinder for a strike mechanism and a guiding pipe for an envil acting upon a tool shaft of a tool formed as a rotary drill. A drill chuck is held on a guiding pipe and extending outwardly beyond a housing and is provided for radial clamping of the tool shaft with at least three displaceable clamping jaws with clamping surfaces for the tool shaft. A rotary drive is provided for the guiding pipe at least for impact drilling.
A hammer drill of the above-mentioned general type is known in the art. One of such hammer drills is disclosed, for example, in the DE-OS No. 3,132,450. Here the drill chuck is arranged fixedly on the guiding pipe. The drill must be inserted into the drill chuck for attaining an unobjectionable clamping, and must have an exact diameter and during impacting drilling operation the anvil strikes both against the tool end and also against the clamping jaws. Even with a small wear or high manufacturing tolerances an unobjectionable clamping and a good rotation are no longer guaranteed.
Another hammer drill is disclosed in the DE-OS No. 2,842,783. Here a drill chuck is disclosed with which the rotary drill with a cylindrical shaft and a hammer drill with a special shaft can be clamped with a profiled cross-section. The hammer drill is not completely clamped because of the axial movability required for transmission of the impact. This known chuck is inserted with the aid of its special shaft in the conventional tool receptacle of a hammer drill which is provided with a play and thereby the exact rotation required for the rotary drill cannot be guaranteed.
The DE-OS Nos. 3,125,444 and 3,125,455 also disclose a hammer drill for drilling and impacting drilling operations in which the tool with a specially shaped shaft is displaceable in an axial direction, but prevented from rotation. However, only tools with a predetermined shaft diameter can be clamped here. The same is true also for a tool holder in accordance with the DE-OS Nos. 1,652,684 and 2,551,125.